Process for the elimination of hydrogen sulfide by using water-in-oil emulsions

ABSTRACT

A process for the removal of hydrogen sulfide present in a composition comprising treating the composition with a water-in-oil emulsion wherein said water-in-oil emulsion containing by weight about: 20 to 80% of a dispersed aqueous phase containing about 20 to 70% of one or more aldehydes chosen from the group constituted by formaldehyde, glyoxal, glutaraldehyde, glycolaldehyde or glyoxylic acid and 80 to 30% of an aqueous solution containing 90 to 100% water and 10 to 0% of a buffer agent pH=5.5±1.5; and 80 to 20% of a continuous oil phase containing about 90 to 99% of one or more saturated and liquid C 6  -C 16  hydrocarbons, and 10 to 1% of an emulsifying system constituted by one or more water-in-oil emulsifying agents.

This is a division of copending parent application Ser. No. 07/577,669,filed 05 Sep. 1990, which has issued as U.S. Pat. No. 5,223,175.

The present invention relates to new water in oil emulsions and theiruse for the elimination of hydrogen sulphide.

Fossil products and notably crude oil, often contain significantquantities of hydrogen sulphide, H₂ S, which it is desirable toeliminate as quickly as possible for it is a toxic, corrosive,inflammable and explosive gas.

It is known to be possible to reduce the hydrogen sulphide contentpresent in aqueous mediums by using aqueous solutions of aldehydes suchas formaldehyde, glyoxal, glutaraldehyde (see for example the U.S. Pat.No. 4,680,127 as well as the references cited in the same document).However, these products take effect slowly even in high proportions.This is therefore a major drawback to their use, notably for thetreatment of crude oil on offshore platforms.

It has now been discovered with astonishment, new compositions obviatingthese inconveniences.

The compositions according to the present invention are characterized inthat they are water-in-oil emulsions containing, by weight, about:

20 to 80% of a dispersed aqueous phase containing about 20 to 70% of oneor more aldehydes chosen from the group constituted by formaldehyde,glyoxal, glutaraldehyde, glycolaldehyde or glyoxylic acid and 80 to 30%of an aqueous solution containing 90 to 100% water and 0 to 10% of abuffer agent to provide a pH=5.5±1.5 and

80 to 20% of a continuous oil phase containing about 90 to 99% of one ormore saturated and liquid C₆ -C₁₆ hydrocarbons, and 10 to 1% of anemulsifying system constituted by one or more water-in-oil emulsifyingagents.

In the present description, oil-in-water emulsifying agent refers to anyconventional water-in-oil emulsifying agent, such as sorbitanmonostearate, sorbitan monooleate, sorbitan sesquioleate and substanceswith so-called weak hydrophilic/lipophilic balance which are alldiscussed in the literature and which are cited notably in theKirk-Othmer Encyclopaedia of Chemical Technology, 3rd edition, volume 8,pages 910-916.

The saturated or liquid C₆ -C₁₆ hydrocarbons can be chosen form thestraight chain or branched C₆ -C₁₆ alkanes and C₆ -C₁₆ cycloalkanesoptionally substituted by one or more linear or branched alkyl groupspreferably containing from 1 to 5 carbon atoms. Preferentially, aparaffin solvent with a C₁₀ -C₁₃ linear chain with a boiling pointcomprised between 180° and 270° C. is used.

Any conventional buffer agents to provide a pH=5.5±1.5 can be used suchas those described in the literature such as the following pairs: aceticacid--sodium acetate, potassium phosphate--sodium citrate, potassiumdihydrogen phosphate--disodium hydrogen phosphate, citric acid--disodiumhydrogen phosphate. Preferentially, an acetic acid--sodium acetatebuffer agent pH=5.5 is used.

More particularly a subject of the invention is the compositions asdefined above, characterized in that the aldehyde is glyoxal.

Notably a subject of the invention is the compositions according to thepresent invention in the form of water in oil emulsions, containing byweight:

60±5% of a dispersed aqueous phase buffered to pH=5.5 with the aceticacid--sodium acetate pair and containing 40 to 50% glyoxal,

40±5% of a continuous oil phase containing 93 to 98% of a saturated andliquid C₁₀ -C₁₃ hydrocarbons mixture and 7 to 2% of an emulsifyingsystem constituted by one or more water in oil emulsifying agents.

Among these compositions, there can be cited more particularly acomposition in the form of a water-in-oil emulsion containing by weight:

60% of an aqueous phase buffered to pH 5.5 and containing about 40%glyoxal,

40% of an oil phase constituted by approximately 95% of a paraffinsolvent with a C₁₀ -C₁₃ linear chain with a boiling point comprisedbetween 180° and 270° C. and 5% sorbitan sesquioleate.

According to the invention, the compositions cited above can be preparedby a process characterized in that the aqueous solution, optionallybuffered to the pH desired, of the chosen aldehyde (or aldehydes) isemulsified in a conventional manner, at ambient temperature, in the oilphase containing in solution the chosen emulsifying agent or agents.

The compositions according to the present invention are endowed withuseful properties for the elimination of hydrogen sulphide present invarious fluids and notably they are particularly effective ateliminating the hydrogen sulphide present in crude oils which can existin the form of water in oil or oil in water emulsions. These propertiesjustify the use of the compositions according to the present inventionin a process for the elimination of hydrogen sulphide present in a fluidwhether liquid or gas, the process characterized in that this fluid istreated with a composition according to the present invention.

In the preferred conditions for implementing the invention, the processdescribed above is carried out at ambient temperature, either by simplemixing of the fluid with the composition of the invention, when it is aliquid, or by bubbling the fluid through the composition of theinvention when it is a gas.

The following examples illustrate the present invention without howeverlimiting it.

The hydrogen sulphide content has been determined by potentiometricdetermination using a silver electrode, according to the followingprocedure:

The following are mixed together at ambient temperature:

100 ml of acetone,

20 ml of isopropyl alcohol,

5 ml of a 20% aqueous solution of ammonium nitrate.

Then, a 50 ml of a sample to be determined, previously de-oxygenated bybubbling nitrogen through it is introduced into this solution which hasbeen carefully de-oxygenated by bubbling nitrogen through it. Thereaction medium obtained is then determined under agitation, in an inertatmosphere, with an aqueous solution of 0.1N silver nitrate, byfollowing the curve of the potential of the mixture as a function of thevolume, V, of the sodium nitrate solution introduced, using apotentiometer equipped with a silver measuring electrode and a referenceelectrode, Ag/AgCl, the external electrolyte of which is an ethanolicsolution saturated with ammonium nitrate. At the balance point, theconcentration of hydrogen sulphide of the sample, expressed in mg/l, isobtained from the equation (1):

EXAMPLE 1

Using a turbine turning at a speed of 10,000 revolutions per minute, 600g of an aqueous solution of glyoxal at 40% by weight is emulsified atambient temperature in a mixture of 380 g of normal C₁₀ -C₁₃ alkaneshaving a boiling point comprised between 180° and 270° C. and 20 g ofsorbitan sesquioleate. Thus 1 kg of a water-in-oil emulsion is obtainedcontaining, by weight, 38% oil, 36% water, 24% glyoxal and 2%emulsifying agent and having at 20° C., a density of 1.05 and aBrookfield viscosity of 240 mPa.s (speed 20 revs/min., axis 2). Thiscomposition contains 4.135 moles of glyoxal, being 4.135 mmoles pergram.

EXAMPLE 2

Using a turbine turning at a speed of 10,000 revolutions per minute, 600g of an aqueous solution containing 240 g (4.135 moles) of glyoxal, 6 gof acetic acid and 6 g of anhydrous sodium acetate and having a pH of5.5 is emulsified at ambient temperature in a mixture of 380 g of normalC₁₀ -C₁₃ alkanes having a boiling point comprised between 180° and 270°C. and 20 g of sorbitan sesquioleate. Thus 1 kg of a water-in-oilemulsion is obtained containing, by weight, 38% oil, 34.8% water, 24%glyoxal, 2% emulsifying agent and 1.2% of buffer, having at 20° C., adensity of 1.05 and a Brookfield viscosity of 260 mPa.s (speed 20revs/min., axis 2). This composition contains 4.135 mmoles of glyoxalper gram.

EXAMPLE 3

One liter of light crude oil from a production well in the North Sea andcontaining 253 mg/l, being 7.42 mmoles/l of hydrogen sulphide, istreated under agitation, at ambient temperature, with either 2 g of acommercially available aqueous solution of glyoxal at 40% by weight,designated A, or 0.5 g or 2 g of the composition described in Example 1,designated Ex 1, and the percentage of hydrogen sulphide eliminated as afunction of time expressed in minutes, is followed by potentiometricdetermination.

The results obtained are given in table 1 in which R represents thehydrogen sulphide/glyoxal molar ratio.

                  TABLE 1                                                         ______________________________________                                                 Proportions                                                                   A          Ex 1                                                      Time       R                                                                  in minutes 0.54         3.59    0.89                                          ______________________________________                                         0          0            0       0                                             5          9           23      42                                            15         22           47      72                                            30         31           52      83                                            60         48           61      92                                            ______________________________________                                    

At the proportion of 2 g/l, the composition according to the inventionallows the virtual total elimination of hydrogen sulphide over 60minutes whilst the aqueous solution of glyoxal A, containing 1.66 timesmore glyoxal, eliminates only half of this in the same time. Thecomposition according to the present invention is therefore clearly moreeffective than an aqueous solution of glyoxal of the prior art.

EXAMPLE 4

One liter of light crude oil from a production well in the North Sea andcontaining 209 mg/l, being 6.13 mmoles/l of hydrogen sulphide, istreated under agitation, at ambient temperature, with either 2 g of acommercially available aqueous solution of glyoxal at 40% by weight,designated A, or 2 g of an aqueous solution of glyoxal buffered atpH=5.5, containing, by weight, 58% water, 40% glyoxal and 2% of a 50/50mixture of acetic acid--anhydrous sodium acetate, designated B, or 0.5 gor 2 g of the composition according to Example 2, designated Ex 2, andthe percentage of hydrogen sulphide eliminated as a function of time isfollowed.

The results obtained are given in table II, in which R represents thehydrogen sulphide/glyoxal molar ratio.

                  TABLE II                                                        ______________________________________                                                  Proportions                                                                   A    B          Ex 2                                                          2 g/l                                                                              2 g/l      0.5 g/l 2 g/l                                       Time        R                                                                 in minutes  0.444  0.444      2.96  0.74                                      ______________________________________                                         0           0      0          0     0                                         5           8     12         28    94                                        15          24     41         49    97                                        30          37     65         55    98                                        60          49     85         65    100                                       ______________________________________                                    

On reading this table, it is noticed that the buffered compositionsaccording to the present invention are particularly effective.

EXAMPLE 5

One liter of a water-in-oil emulsion from an oil well in the Parisianregion, containing by weight 70% oil, 30% water and 241 mg/l, being 7.07mmoles/l, of hydrogen sulphide is treated under agitation, at ambienttemperature with 2 g either of a commercially available aqueous solutionof glyoxal at 40% by weight, or with the composition of Example 2 andthe percentage of hydrogen sulphide eliminated as a function of time isfollowed as in the previous examples.

The results obtained are listed in table III in which R represents thehydrogen sulphide/glyoxal molar ratio.

                  TABLE III                                                       ______________________________________                                                       Proportions                                                                   A    Ex 2                                                                     2 g/l                                                                              2 g/l                                                     Time             R                                                            in minutes       0.51   0.85                                                  ______________________________________                                         0                0      0                                                     1                0     72                                                     5               10     87                                                    15               19     89                                                    30               30     90                                                    60               45     95                                                    ______________________________________                                    

These results show the high efficiency of the compositions of thepresent invention in eliminating the hydrogen sulphide present in awater-in-oil emulsion.

EXAMPLE 6

Using the operating method of Example 1, a water-in-oil emulsion isprepared containing, by weight, 38% oil, 37.8% water, 22.2% formaldehydeand 2% sorbitan sesquioleate starting from an aqueous solution offormaldehyde at 37% by weight and normal C₁₀ -C₁₃ alkanes. The emulsionobtained has a density at 20° C. of 0.95 and a Brookfield viscosity of55 mPa.s determined at 20° C. at the speed of 20 revs/min. with axis 1.

EXAMPLE 7

Similarly, using the operating method described in Example 1, awater-in-oil emulsion is prepared containing, by weight, 38% oil, 30%glyoxylic acid, 30% water and 2% sorbitan sesquioleate starting from acommercially available aqueous solution of 50% glyoxylic acid and normalC₁₀ -C₁₃ alkanes. The emulsion obtained has a density at 20° C. of 1.07and a Brookfield viscosity of 105 mPa.s determined at 20° C. at thespeed of 20 revs/min. with axis 2.

EXAMPLE 8

The effectiveness of the emulsion obtained in Example 6 was comparedwith that of a commercially available aqueous solution of formaldehydeat 37% by weight, designated C, in the proportion of 2 g/l, on a lightcrude oil from a production well in the North Sea containing 234 mg/l ofH₂ S. The results obtained are listed in table IV.

EXAMPLE 9

Similarly the effectiveness of the emulsion obtained in Example 7 wascompared to that of a commercially available aqueous solution ofglyoxylic acid at 50% by weight, designated D, in the proportion of 2g/l on the same light crude oil used in Example 8. The results obtainedare given in table IV.

                  TABLE IV                                                        ______________________________________                                        Percentages of the elimination of H.sub.2 S as a function of                  time.                                                                         Time in      Products                                                         minutes      Ex. 6  C          Ex. 7                                                                              D                                         ______________________________________                                         0            0      0          0    0                                         5           25      5          6    5                                        15           39     14         18   17                                        30           71     24         24   21                                        60           87     33         38   32                                        ______________________________________                                    

It is noted that the compositions according to the present invention aremore efficient than the aqueous solution of glyoxylic acid or of theformaldehyde used for their preparation.

I claim:
 1. A process for the removal of hydrogen sulphide present in a composition comprising treating said composition with a water-in-oil emulsion,wherein said emulsion comprises about: 20-80% by weight of a dispersed aqueous solution comprising about 20 to 70% by weight of an aldehyde selected from the group consisting glyoxal, formaldehyde, glutaraldehyde, glycolaldehyde and glyoxylic acid, and about 80 to 30% by weight of water and at least one of acetic acid or sodium acetate in a quantity sufficient to provide a buffered pH of 5.5±1.5 and, 80 to 20% by weight of a continuous oil phase comprising about 90 to 99% by weight of one or more saturated and liquid C₆ -C₁₆ hydrocarbons, and about 10 to 1% by weight of an emulsifying system comprising one or more water-in-oil emulsifying agents.
 2. A process according to claim 1, wherein said aldehyde is glyoxal.
 3. A process according to claim 1, wherein said emulsion comprises,6± 5% by weight of a dispersed aqueous solution comprising about 40 to 50% by weight of glyoxal, about 60 to 50% by weight of water and at least one of acetic acid or sodium acetate in a quantity sufficient to provide a buffered pH of about 5.5 and, 40%±5% by weight of a continuous oil phase comprising about 93 to 98% by weight of one or more saturated and liquid C₁₀ -C₁₃ hydrocarbons, and about 7 to 2% by weight of an emulsifying system comprising one or more water-in-oil emulsifying agents.
 4. A process according to claim 3, wherein said emulsion comprises, about60% by weight of a dispersed aqueous solution comprising about 40% by weight of glyoxal and about 60% by weight of water and at least one of acetic acid or sodium acetate in a quantity sufficient to provide a buffered pH of about 5.5 and, 40% by weight of a continuous oil phase comprising about 95% by weight of a paraffin solvent with a C₁₀ -C₁₃ linear chain with a boiling point between 180° and 270° C. and 5% sorbitan sesquinoleate.
 5. A process according to claim 3, wherein said composition being treated is a gas.
 6. A process according to claim 5, wherein said treating comprises bubbling said gas through said emulsion.
 7. A process according to claim 3, wherein said composition being treated is a liquid.
 8. A process according to claim 7, wherein said treating comprises mixing said liquid with said emulsion.
 9. A process according to claim 3, wherein said composition being treated is a solid.
 10. A process according to claim 1, wherein said composition being treated is a gas.
 11. A process according to claim 10, wherein said treating comprises bubbling said gas through said emulsion.
 12. A process according to claim 1, wherein said composition being treated is a liquid.
 13. A process according to claim 12, wherein said treating comprises mixing said liquid with said emulsion.
 14. A process according to claim 1, wherein said composition being treated is a solid.
 15. A process according to claim 1, wherein said aldehyde is glyoxal. 